Lightning Tree is your #1 choice and should be chosen at lvl3 - Warp Armor is an excellent passive that grants great stats. T-stone is good against bosses which you don't really want to fight in melee (starting from the Smith, ending with Astrogha)
Cold Tree - 25% DR from minions that also provide good tanking (very helpful in Terror Fauzt, Legacy of Blood etc.). With Snow Queen + Warp Armor combo your total defence can be equal to a melee necro/pouncezon with average gear = low chance to be hit). Though you can use your blade spirits as minions instead.
Fire Tree - excellent passive that grant huge life regen, should be fully smaxed (use all possible sources of max skill lvl increased by); Firedance greatly boosts your elemental damage from spells - for example, if you're using Grizzly secret warp blade, this tree is a must.
Poison - Hive is fine as well as Crushing Blow from the passive skill, but, from my experience, you'll need more careful playing with choosing this tree.
TL,DR - Cold + Lightning - defensive style; Fire + Lightning = balanced; Poison + Lightning = offensive.
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